Digital microwave radios have become particularly advantageous in a number of key types of communication. High frequency point to point communications are used by, among others, cellular operators, telecommunications operators, private network operators, governments, and large telecommunications operations.
Typical of conventional digital microwave radios is the use of a separate transmitter (TX) module and a separate receiver (RX) module. Although conventional radios have the ability to tune over a vast frequency range, the problems caused by interaction between the TX and RX modules necessitate limiting that range. Limiting the range is necessary due to two factors. First, the sensitivity of the circuitry of the RX module, and the common use of an antenna by both the TX and RX modules, mandate separation of the passbands for RX and TX filters to prevent TX power from interfering with the RX module. Interference with the RX module will generally cause saturation and intermodulation products. Second, image frequencies presented at the antenna port can generate RX interference. Thus, it is necessary to use band limiting filters to reject the image frequencies. Image frequencies are located at either plus or minus twice the first intermediate frequency from the desired receiver frequency.
Conventional digital microwave radios, as shown in FIG. 1, include a filter assembly 107 mounted within radio enclosure 100. Although, the filter assembly 107 including a TX filter 106, circulator 108 and RX filter 114 may facilitate selection of a specific frequency range, placement of the filter assembly 107 within the enclosure 100 subjects the manufacture, installation and implementation of the radio to numerous limitations. One limitation is that tuning conventional digital microwave radios to a set frequency range must occur during the manufacturing process. Another limitation is that retuning a conventional digital microwave radio requires the difficult and costly process of disassembling the radio, replacing and adjusting the filter assembly 107, and reassembling the radio. Particularly due to the complexity of the retuning process, a technician will likely need to remove the radio from a client's site to perform the channel modifications at a manufacturer's site. Another limitation is that due to the configuration of a conventional radio, tuning the radio to a specific operational bandwidth generally requires replacement or removal of a plurality of parts such as waveguide elbows.
Returning to FIG. 1, typically a conventional digital microwave radio includes TX 102 and an RX 110 modules that have a waveguide flange (104 & 112) at either end of a common circulator 108 and separate internal filters (106 & 114). Generally the output of the circulator 108 is offset 90 degrees from the centerline of the branching filter assembly 107.
The branching filter assembly 107 radio is generally configured in a collinear assembly, although the branching filter assembly 207 of other conventional digital microwave radios, as shown in FIG. 2, may be configured in a U-shaped assembly. FIG. 2 shows an example of other conventional digital microwave radios that include waveguide elbows (205 & 209), and an RX module 210 and a TX module 202 with each correspondingly mounted to separate flanges 212 and 204.
The angle of each waveguide and the dimensions of the waveguide elbows are chosen to cause a specific polarization effect for coupling the power of the microwave signal. For example, FIG. 2 shows a radio providing two waveguide elbows with 90 degree angles to couple the power of the microwave signals. In FIG. 1, the circulator 108 provides an RX and TX interface at 90 degrees toward the centerline of the antenna 116, and in FIG. 2, the circulator 208 similarly provides an RX and TX interface at 90 degrees toward the centerline of the antenna 216.
The mechanical mounting arrangement of the conventional digital microwave radios of FIG. 1 and FIG. 2 subject the manufacture of radios to a number of limitations. For example, the mounting arrangements of conventional radios generally are too large to encase these radios in compact enclosures. Further, the TX and RX modules of conventional radios may not be mounted to a common heat sink. Further, since conventional radios include numerous components such as wageguide elbows and circulators, it is a costly process to manufacture conventional radios. Still further, retuning a conventional radio requires the costly modification or replacement of a plurality of components. For instance, tuning a conventional radio may require modification or replacement of components such as the filters, waveguide elbows and circulators (See FIGS. 1 and 2).
As a result, there has been a longfelt need for a digital microwave radio which includes a mechanical mounting arrangement that avoids the need for large unit enclosures, and the costly and timely process of retuning a radio at a manufacture site that generally includes modifying or replacing a plurality of components internally assembled within the radio enclosure--requirements long associated with conventional digital microwave radios.